The present invention relates to improved smoke detectors adapted to a smoke sensing apparatus comprising a smoke detector and an electric indicating or alarming device including a relay such as, for example, a control electric valve the control electrode of which is connected to the output terminal of said smoke detector, and more particularly to smoke detectors in which a kind of radioactive substance is used in common in two ionization chambers.
Hitherto, as a method of detecting particles contained in any kind of smoke, it has been well known to utilize ionization of said particles. For this purpose, a smoke detector provided with two inner and outer ionization chambers each including a radioactive substance therein has been generally used, said outer chamber being denoted as an outer ionization chamber and being provided with a metal wire net for passing outer gas therethrough, and said inner chamber being denoted as an inner ionization chamber and being constructed so that penetration of said outer gas into said inner ionization chamber is very difficult.
In the conventional smoke detectors as mentioned above, there are disadvantages such that the detector becomes large in its structure, very complicated in its construction, and uneconomical because each of the inner and outer ionization chambers is provided with a radioactive substance therein, and, furthermore, the quantity of the radioactive rays is relatively large, thereby increasing harmful effects on human bodies.
Furthermore, in the conventional smoke detectors as mentioned above, precise detection at various temperature condition or precise detection unaffected by variation of the surrounding temperature is very difficult and simple temperature compensation or alarming of an emergency temperature itself cannot be attained. For the purpose of temperature compensation of the smoke detectors, various compensating circuits utilizing any kind of various thermistors have been conventionally utilized, but these circuits are relatively complex and cause expensive structure of the smoke detector provided with said circuit.